Cryptography – Communication system using cryptography – Frequency shift or inversion
Patent
1989-12-26
1991-01-08
Tarcza, Thomas H.
Cryptography
Communication system using cryptography
Frequency shift or inversion
370120, 380 38, H04K 104
Patent
active
049842196
ABSTRACT:
A method and apparatus for decoding of frequency inversion based scramblers is disclosed. A quadrature amplitude modulation detector determines the frequency of the tone used for inverting the scrambled signal by determining which of a plurality of quadrature detector pairs, each using a different conversion frequency, has the greatest magnitude difference between the quadraturely related signals. The frequency of the quadrature pair with the greatest difference is the frequency of the inverting tone during the inverting period of time. This frequency information is used to generate a reinversion tone to unscramble the scrambled signal.
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Van Lannep et al., "Frequency Inversion Scrambler Uses Micro-Processed SSB Audio", Mobile Radio Technology, Aug. 1984, pp. 34-40.
Dennis, "Who's Got a Secret?", Communications, Sep. 1984, pp. 62,63,68,69,70.
Brown Daniel P.
Puhl Larry C.
Hackbart Rolland R.
Jenski Raymond A.
Motorola Inc.
Swann Tod
Tarcza Thomas H.
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